I've made my first novel, Ventus, available as a free download, as well as excerpts from two of the Virga books. I am looking forward to putting up a number of short stories in the near future.

Complete novel: Ventus

To celebrate the August, 2007 publication of Queen of Candesce, I decided to re-release my first novel as an eBook. You can download it from this page. Ventus was first published by Tor Books in 2000, and and you can still buy it; to everyone who would just like to sample my work, I hope you enjoy this version.

I've released this book under a Creative Commons license, which
means you can read it and distribute it freely, but not make derivative
works or sell it.

Book Excerpts: Sun of Suns and Pirate Sun

I've made large tracts of these two Virga books available. If you want to find out what the Virga universe is all about, you can check it out here:

Major Foresight Project: Crisis in Zefra

In spring 2005, the Directorate of Land Strategic Concepts of National Defense Canada (that is to say, the army) hired me to write a dramatized future military scenario. The book-length work, Crisis in Zefra, was set in a mythical African city-state, about 20 years in the future, and concerned a group of Canadian peacekeepers who are trying to ready the city for its first democratic vote while fighting an insurgency. The project ran to 27,000 words and was published by the army as a bound paperback book.

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A tale of two worlds: habitable, or colonizable?

Habitability is the measure of highest value in planet-hunting. But should it be?

Kepler and the other planet-finding missions have begun to bear fruit. We now know that most stars have planets, and that a surprising percentage will have Earth-sized worlds in their habitable zone--the region where things are not too hot and not too cold, where life can develop. Astronomers are justly fascinated by this region and what they can find there. We have the opportunity, in our lifetimes, to learn whether life exists outside our own solar system, and maybe even find out how common it is.

We have another opportunity, too--one less talked-about by astronomers but a common conversation among science fiction writers. For the first time in history, we may be able to identify worlds we could move to and live on.

As we think about this second possibility, it's important to bear in mind that habitability and colonizability are not the same thing. Nobody seems to be doing this; I can't find any term but habitability used to describe the exoplanets we're finding. Whether a planet is habitable according to the current definition of the term has nothing to do with whether humans could settle there. So, the term applies to places that are vitally important for study; but it doesn't necessarily apply to places we might want to go.

Whether a planet is habitable according to the current definition of the term has nothing to do with whether humans could settle there.

To see the difference between habitability and colonizability, we can look at two very different planets: Gliese 581g and Alpha Centauri Bb. Neither of these is confirmed to exist, but we have enough data to be able to say a little about what they're like if they do. Gliese 581g is a super-earth orbiting in the middle of its star's habitable zone. This means liquid water could well form on its surface, which makes it a habitable world according to the current definition.

Centauri Bb, on the other hand, orbits very close to its star, and its surface temperature is likely high enough to render one half of it (it's tidally locked to its sun, like our moon is to Earth) a magma sea. Alpha Centauri Bb is most definitely not habitable.

So Gliese 581g is habitable and Centauri Bb is not; but does this mean that 581g is more colonizable than Bb? Actually, no.

Because 581g is a super-earth, the gravity on its surface is going to be greater than Earth's. Estimates vary, but the upper end of the range puts it at 1.7g. If you weigh 150 lbs on Earth, you'd weigh 255 lbs on 581g. This is with your current musculature; convert all your body fat to muscle and you might just be able to get around without having to use leg braces or a wheelchair. However, your cardiovascular system is going to be under a permanent strain on this world--and there's no way to engineer your habitat to comfortably compensate.

On the other hand, Centauri Bb is about the same size as Earth. Its surface gravity is likely to be around the same. Since it's tidally locked, half of its surface is indeed a lava hell--but the other hemisphere will be cooler, and potentially much cooler. I wouldn't bet there's any breathable atmosphere or open water there, but as a place to build sealed domes to live in, it's not off the table.

Also consider that it's easier to get stuff onto and off of the surface of Bb than the surface of a high-gravity super-earth. Add to that the very thick atmosphere that 581g is likely to have, and human subsistence on 581g--even if it's a paradise for local life--is looking more and more awkward.

Doubtless 581g is a better candidate for life; but to me, Centauri Bb looks more colonizable.

A definition of colonizability

We've got a fairly good definition of what makes a planet habitable: stable temperatures suitable for the formation of liquid water. Is it possible to develop an equally satisfying (or more satisfying) definition of colonizability for a planet?

Yes--and here it is. Firstly, a colonizable world has to have an accessible surface. A super-earth with an incredibly thick atmosphere and a surface gravity of 3 or 4 gees just isn't colonizable, however much life there may be on it.

Secondly, and more subtly, the right elements have to be accessible on the planet for it to be colonizable. This seems a bit puzzling at first, but what if Centauri Bb is the only planet in the Centauri system, and it has only trace elements of Nitrogen in its composition? It's not going to matter how abundant everything else is. A planet like this--a star system like this--cannot support a colony of earthly life forms. Nitrogen is a critical component of biological life, at least our flavour of it.

In an article entitled "The Age of Substitutibility", published in Science in 1978, H.E. Goeller and A.M. Weinberg proposed an artificial mineral they called Demandite. It comes in two forms. A molecule of industrial demandite would contain all the elements necessary for industrial manufacturing and construction, in the proportions that you'd get if you took, say, an average city and ground it up into a fine pulp. There're about 20 elements in industrial demandite including carbon, iron, sodium, chlorine etc. Biological demandite, on the other hand, is made up almost entirely of just six elements: hydrogen, oxygen, carbon, nitrogen, phosphorus and sulfur. (If you ground up an entire ecosystem and looked at the proportions of these elements making it up, you could in fact find an existing molecule that has exactly the same proportions. It's called cellulose.)

Thirdly, there must be a manageable flow of energy at the surface. The place can be hot or cold, but it has to be possible for us to move heat around. You can't really do that at the surface of Venus, for instance; it's 800 degrees everywhere on the ground so your air conditioning spends an insane amount of energy just overcoming this thermal inertia. Access to a gradient of temperature or energy is what makes physical work possible.

Obviously things like surface pressure, stellar intensity, distance from Earth etc. play big parts, but these are the main three factors that I can see. It should be instantly obvious that they have almost nothing to do with how far the planet is from its primary. There is no 'colonizable zone' similar to a 'habitable zone' around any given star. The judgment has to be made on a world by world basis.

Note that by this definition, Mars is marginally colonizable. Why? Not because of its temperature or low air pressure, but because it's very low in Nitrogen, at least at the surface. The combination of Mars and Ceres may make a colonizable unit, if Ceres has a good supply of Nitrogen in its makeup--and this idea of combo environments being colonizable complicates the picture. We're unlikely to be able to detect an object the size of Ceres around Alpha Centauri, so long-distance elimination of a system as a candidate for colonizability is going to be difficult. Conversely, if we can detect the presence of all the elements necessary for life and industry on a roughly Earth-sized planet, regardless of whether it's in its star's habitable zone, we may have a candidate for colonizability.

The colonizability of an accessible planet with a good temperature gradient can be rated according to how well its composition matches the compositions of industrial and biological demandite. We can get very precise with this scale, and we probably should. It, and not habitability, is the true measure of which worlds we might wish to visit.

To sum up, I'm proposing that we add a second measure to the existing scale of habitability when studying exoplanets. The habitability of a planet actually says nothing about how attractive it might be for us to visit. Colonizability is the missing metric for judging the value of planets around other stars.

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I like very much the distinction between habitability and colonizability, it makes sense. I would like to challenge a bit the concept a world must have an acessible surface to be colonizable. I assume acessible here means the colony would actually have to be built on solid ground.

There has been a lot of talk about building aerostats in Venus´ upper atmosphere, where temperature and pressure are closer to Earth´s. In this case, there would be an acessible surface - we have dropped probes on Venus, and probably we can drop stuff like mining equipment or whatever there for short periods - but we would not live on it, but rather in the clouds 50 km above it. The "colonization combo" would be using Venus' reduced Delta-V requirement to reach the Asteroid Belt to supply the colony with whatever is needed. Lots of elements could be scooped off the atmosphere, including hydrogen and oxygen, and there are many ways produce energy there, like wind turbines and such.

Anyway, my point here is that perhaps solid ground is not an absolute requirement for colonizability. It helps a lot for sure, but as any environment which does not allow short sleeve work in the open would required sealed habitats and life support anyway, putting such habitat to float in the upper clouds of a planet maybe is not so far-fetched...

"If you ground up an entire ecosystem and looked at the proportions of these elements making it up, you could in fact find an existing molecule that has exactly the same proportions. It's called cellulose".

Not really. Cellulose = (CH20)n. The ecosystem has a lot of N in proteins, and P in nucleic acids.

Hi Karl
I've been making a similar complaint about the way science media uses "habitable" making it practically equal to "livable" - as in unmodified humans living in the open. In the literature a "habitable planet" has liquid water on the surface - and that's it. As the greenhouse gas of choice is carbon dioxide in most analyses that means most "habitable planets" would probably exceed the toxic limit for carbon dioxide, as they require multi-bar levels of CO2 to be "habitable" over most of the "habitable zone" (just recently re-defined as 0.99-1.7 AU.) A bit further out from stars is the "hydrogen greenhouse zone" - planets which can have oceans of water thanks to several bars of hydrogen. By one analysis such planets can sustain photosynthetic ecosystems out to ~10 AU, though anything that starts eating hydrogen quicker than it can be replaced will ultimately freeze the planet.

While such planets can be colonized, none would count as "livable" in the "Star Trek" M-class planet sense. Such planets will huddle close to 1 AU (or equivalent) and be much rarer than their less Earth-like cousins. Or so our models tell us.

I'm a member of the Association of Professional Futurists with my own consultancy, and am also currently Chair of the Canadian node of the Millennium Project, a private/public foresight consultancy active in 50 nations. As well, I am an award-winning author with ten published novels translated into as many languages. I write, give talks, and conduct workshops on numerous topics related to the future, including:

I use Science Fiction to communicate the results of actual futures studies. Some of my recent research relates to how we'll govern ourselves in the future. I've worked with a few clients on this and published some results.

Here are two examples--and you can read the first for free:

The Canadian army commissioned me to write Crisis in Urlia, a fictionalized study of the future of military command-and-control. You can download a PDF of the book here:

Crisis in Urlia

For the "optimistic Science Fiction" anthology Hieroglyph, I wrote "Degrees of Freedom," set in Haida Gwaii. "Degrees of Freedom" is about an attempt to develop new governing systems by Canadian First Nations people.

I'm continuing to research this exciting area and would be happy to share my findings.

Year 2015

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“Bulging with complex ideas and extrapolations … amazing."—Kirkus Reviews
“The interrelationship between technology and philosophy that informs [Livia's] choice gives depth and breadth to a book that many will want to reread to get all the nuances.”
—Publishers Weekly
“Schroeder continues to improve his unique blend of hard SF and vivid, dreamlike prose and bids fair to become a major genre voice.”
—Booklist

Sheer Fun: The Virga Series

(Sun of Suns and Queen of Candesce are combined in Cities of the Air)

“An adventure-filled tale of sword
fights and naval battles... the real fun of this coming-of-age tale includes a
pirate treasure hunt and grand scale naval invasions set in the cold, far
reaches of space. ” —Kirkus Reviews (listed in top 10 SF novels for 2006)

"With Queen of Candesce, [Schroeder] has achieved a clockwork balance of deftly paced adventure and humour, set against an intriguing and unique vision of humanity's far future.--The Globe and Mail

"[Pirate Sun] is fun in the same league as the best SF ever has had to offer, fully as exciting and full of cool science as work from the golden age of SF, but with characterization and plot layering equal to the scrutiny of critical appraisers."--SFRevu.com

"...A rollicking good read... fun, bookish, and full of insane air battles"--io9.com

"A grand flying-pirate-ship-chases-and-escapes-and-meetings-with-monsters adventure, and it ends not with a debate or a seminar but with a gigantic zero-gee battle around Candesce, a climactic unmasking and showdown, just desserts, and other satisfying stuff."--Locus